In a typical wireless communications environment, an user equipment (UE) may communicate voice and/or data signals with one or more service networks via cellular stations (or referred to as evolved Node-Bs (eNBs) of service networks. The wireless communications between the UE and the service networks may be in compliance with various wireless technologies, such as the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA 2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, LTE-Advanced (LTE-A) technology, and others.
As one of next-generation wireless communications systems, the Third Generation Partnership Project (3GPP) LTE provides technologies for high data rates and system capacity. Further, LTE-A is defined to support new components for LTE to meet higher communications demands. Device-to-Device (D2D) communications is a technology component for LTE-A. D2D communications enables two or more devices in proximity of each other, that could be called proximity devices or neighboring devices, to establish direct local links, either in an autonomous manner to form an ad hoc network or coordinated by a base station, and to setup communications and/or to perform direct data transfer.
However, there are many issues to be addressed before the concept of D2D communications can be implemented and commercialized. One of the issues is how to find device proximity. Recently, the 3GPP has researched proximity based services (ProSe) for D2D communications in LTE wireless communications system. However, the existing solution for distributed D2D proximity discovery in the LTE wireless communications system is less likely to see. Moreover, in current LTE wireless communications system, separate signaling messages must be used for finding D2D device(s) with sufficient signal strength, finding D2D device(s) with the same application interest/requirement and synchronization among the D2D devices.